Ventilation assisted passive cell freezing device

ABSTRACT

A system and method for concurrently and uniformly removing thermal energy from clustered specimen samples.

This application is a Continuation of U.S. patent application Ser. No.14/118,542, filed Nov. 18, 2013, entitled VENTILATION ASSISTED PASSIVECELL FREEZING DEVICE, which is a National Stage of InternationalApplication No. PCT/US2012/038431, filed May 17, 2012, and entitledVENTILATION ASSISTED PASSIVE CELL FREEZING DEVICE, which claims thebenefit of U.S. Provisional Application No. 61/487,445, filed May 18,2011, and entitled VENTILATION ASSISTED PASSIVE CELL FREEZING DEVICE.This application claims priority to and incorporates herein by referencethe above-referenced applications in their entirety.

BACKGROUND OF THE INVENTION

Maximizing the percentage of suspended cells recovered live followingfreezing, archival storage, and thawing requires that a specifictemperature reduction profile be applied (see U.S. Patent ApplicationPub. No. 2011/0308271 and PCT Pub. No. 2011/159934, each of which isincorporated herein by reference). When freezing multiple vialsconcurrently, it is therefore critical that each vial experience thesame desired profile. While passive cell freezing systems offer asignificant cost savings over actively managed temperature reductionsystems, current passive freezing system designs that offer vialfreezing rate uniformity depend upon a circular array of the vials toproduce uniform thermal energy release to the surrounding environment.The need for a circular array places a practical limit on the number ofvials that can be contained in a freezing unit, as the circumference ofthe device increases in a linear proportion to the number of vialscontained therein.

The sample vials may be confined in a densely packed array; however,this arrangement will require that, for a portion of the vials, the pathof heat transfer will at least partially be directed through or pastadjacent vials, thereby imposing a variable thermal gradient environmentfor the vial collection during the freezing process. This condition willinevitably result in a spectrum of temperature reduction profiles, onlya fraction of which may be appropriate for optimal cell viability uponthawing. In addition, as the number of vials in the cluster isincreased, so will the thermal mass of the collection. To maintain thedesired temperature reduction profile, a greater quantity of thermalenergy will need to be released per unit time, thereby necessitating areduction in the thickness of the insulation of the passive coolingdevice, thereby imposing an even greater imbalance in the freezing ratesbetween the exterior and interior vials of the cluster.

As the sample capacity of the freezing device is increased, a secondaryproblem arises in that, upon completion of the freezing process, thesamples will need to be transferred to archival storage. Transferringthe vials individually is both time consuming and presents opportunityfor frozen specimens to warm, thereby presenting a great threat to theintegrity and viability of the frozen cells.

Thus, there remains a need for passive cooling/freezing devices toachieve the desired temperature reduction profile for clustered samplevials. The present invention meets this need.

SUMMARY OF THE INVENTION

The present invention provides an insulating chamber that surrounds acluster of sample vials and their contents. In some embodiments, thechamber is constructed from an insulating material such as polyethylene,styrene, or urethane foam. The insulating chamber further comprises agas inlet port and a gas outlet port, wherein the gas inlet port islocated at or near an underside of the chamber, and wherein the gasoutlet port is located at or near a top side of the chamber. The gasports may further be configured to receive restrictors or baffles forthe purpose of regulating the flow of gases through the gas ports. Insome embodiments, the restrictors contain a single hole or port; inother embodiments, the restrictors contain a plurality of holes orports. The cross-sectional shape and size of the gas ports may furtherbe adjusted to provide a desired amount of gas flow or fluid dynamic. Inother embodiments the gas ports may comprise one or more valves for thepurpose of regulating gas flow into and out of the chamber. In someembodiments, valves are provided which may be manually adjustable forthe purpose of gas flow regulation. The chamber may further comprise twoor more interlocking sections to facilitate placement and removal ofsample vials within the chamber.

In some embodiments, the cluster of sample vials within the chamber iscontained or stored within a removable rack. When inserted within thechamber, the removable rack acts to divide the interior of the chamberinto an upper and lower chamber. In many embodiments, the rack restsdirectly upon an interior, annular rim protrusion which forms a portionof an interior wall surface of the chamber. The rim protrusion may bepositioned such that the interior of the chamber is divided into upperand lower chambers by the rim. The upper and lower chambers may befurther spatially defined by placement of the removable rack onto therim protrusion, wherein the removable rack provides a physical barrierbetween the two chambers.

Various embodiments of the present invention provide a gaseous pathwaythrough the interior of the chamber and the removable rack. For example,a gas (typically air) may enter the lower chamber via the one or moreports and pass into the upper chamber via gas vents provided in theremovable rack. The lower chamber is further configured such that a gasenters the lower chamber via the inlet port and flows through the gasvents of the removable rack and into the upper chamber.

Gas flow through the insulating chamber is facilitated by thermodynamicprinciples. For example, when the device is placed in a freezer, coldgas introduced into the lower chamber via the inlet port forces warm gasfrom the lower chamber, through the removable rack and into the upperchamber. Excess cold gas within the lower chamber is forced though theremovable rack and into the upper chamber, thereby forcing warm gaswithin the upper chamber to exit the insulating chamber through theoutlet port. Heat is removed from the vial samples by the cold gas,thereby warming the gas surrounding the sample vials. The warmed gas isless dense than the cold gas, so the cold gas entry causes the warmedgas to move upwardly into the upper chamber and exit the device via theoutlet port. As the warmed gas exits the upper chamber, additional coldgas is drawn into the lower chamber via the inlet port. The introductionof cold gas into the lower chamber forces warmer gas within the lowerchamber to pass through the removable rack and into the upper chamber,thereby continuing the cooling process. The exchange of gases within theupper and lower chamber ceases once temperature equilibrium is reachedbetween the lower chamber, the upper chamber, the vial samples, and theexterior environment.

In some embodiments, the outlet port comprises a one-way port, such thatgas is prevented from entering the upper chamber via the outlet port.Rather, gas is permitted to enter the upper chamber solely by passingthrough the gas vents from the lower chamber. Further, in some instancesthe input port comprises a one-way port, such that gas is prevented fromexiting the lower chamber via the input port. Rather, gas within thelower chamber must exit the device through the outlet port after passingthrough the gas vents of the removable rack and the upper chamber.

In some embodiments, the sample vial rack comprises a plurality of wellsor openings for the purpose of receiving one or more sample vial tubes.In other embodiments, the rack forms an airtight seal with the rim suchthat gas must pass through the gas vents of the removable rack to movebetween the upper and lower chambers. For example, the removable rack insome embodiments comprises a continuous surface having a size and shapecompatible interface with the rim protrusion around the perimeter of thechamber. The wells or opening are configured in some embodiments tomaximize or minimize contact with the sample vial. For example, in someembodiments the removable rack comprises a thermoconductive material,such that the temperature of the vial sample is in part regulated by thetemperature of the removable rack. In these embodiments, one canmaximize surface contact between the vial sample and the opening or wellof the rack. In other instances, the removable rack comprises athermally inert material, such that the temperature of the vial sampleis regulated primarily by contact with the gas within the insulatingchamber. Accordingly, in these latter embodiments, one can limit contactbetween the removable rack and the sample vial, and so maximize exposureof the vial sample to the gas within the insulating chamber. The rackmay further comprise one or more holes positioned between selected vialsfor the purpose of directing gas flow around the sample vials, ordirectly into contact with the sample vials. In various embodiments, therack is composed of polypropylene or polyethylene or plastic blends ofthose two polymers as the main or only components.

In some embodiments, the sample rack and sample vial payload may betransferred as a single unit to an archival storage site, such as asample freezer. As such, some systems of the present invention eliminatethe need to transfer sample vials to an archival storage siteindividually.

In some embodiments, the sample vials are introduced into the removablerack after the removable rack is seated within the insulating chamber onthe rim protrusion. In other instances, the sample vials are firstloaded into the removable rack and then introduced into the insulatingchamber by placing the removable rack into the insulating chamber. Theinsulating chamber includes a base and lid or cover, wherein uponplacing the cover over the base (in some embodiments, the cover and baseare configured to interlock when closed), the removable rack is enclosedwithin the insulating chamber, which then can be placed into anenvironment of reduced temperature. As the environmental gases in thereduced temperature environment will be of greater density than thewarmer gases contained within the interior of the insulating chamber,colder gases will enter through the underside vent and displace thegases of greater temperature and lesser density which will in turn exitthrough the top vent. As the cold gases contact the warmer sample vials,thermal energy will be transferred to the gases from the vials. Upongaining thermal energy, the gases will be reduced in density and becomedisplaced by a continuous influx of colder gas. As such, by selectiveplacement of gas passage holes in the rack surface, thermal energy maybe removed from specific vials in the central portion of the vialcluster, thereby equalizing the rate of thermal energy loss from allvials contained within the chamber of the invention. The overall rate ofthermal energy loss, and therefore the rate of sample vial temperaturereduction, can be adjusted by various combinations of vent restriction,rack gas passage hole size and placement, and chamber insulationthickness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a sample freezing apparatus and removablerack in accordance with a representative embodiment of the presentinvention.

FIG. 2 is a cross section perspective view of an assembled samplefreezing apparatus and removable rack in accordance with arepresentative embodiment of the present invention.

FIG. 3 is a top view of the base of a sample freezing apparatus, aremovable rack, and sample vials in accordance with a representativeembodiment of the present invention.

FIG. 4 is a graphic representation of the freezing rates of three vialsrepresenting three concentric distances from the vial cluster center,demonstrating the ability of air flow compensation both to acceleratethe overall freezing rate and to equalize the freezing rates within thevial cluster, in accordance with a representative embodiment of thepresent invention.

FIG. 5 is a cross section perspective view of an assembled samplefreezing apparatus and removable rack with sample vials in accordancewith a representative embodiment of the present invention.

FIG. 6 is a dimensioned front cross section perspective view of anassembled sample freezing apparatus and removable rack with sample vialsin accordance with a representative embodiment of the present invention.

FIG. 7 is a multi-perspective graphic representation of the sample vialrack of the freezing apparatus shown in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described with regard to the accompanyingdrawings, which assist in illustrating various features of theinvention.

Referring now to FIG. 1, a sample freezing apparatus 100 is shown.Sample freezing apparatus 100 generally comprises an enclosure having aninternal, insulating chamber in which a removable rack 130 is placed andenclosed. The insulating chamber of sample freezing apparatus 100generally comprises a thermo-insulating material, such as polyethylene,polystyrene, or polyurethane foam materials. The insulating chamber mayfurther include additional materials to enhance or otherwise optimizethe insulating needs of the device. For example, apparatus 100 maycomprise additional internal or external insulating material to provideadditional insulation. Alternatively, apparatus 100 may comprise one ormore compartments or lines for the addition of a cooling agent, such asliquid nitrogen or a pre-cooled ballast mass.

In some embodiments, sample freezing apparatus 100 comprises a base 120having a top end comprising an opening having a perimeter surface forcompatibly receiving a lid or cover 110. Lid 110 generally comprises abottom end having an opening comprising a perimeter surface forcompatibly interconnecting with the top end of base 120. Base 120 andlid 110 are thus configured to interconnect compatibly, therebyisolating the internal, insulating chamber from an exterior environment102 surrounding the apparatus 100. Base 120 may further comprise one ormore legs or supports, whereby to provide clearance between a bottomsurface of base 120 and a surface on which base 120 is supported.

Base 120 further comprises an internal surface for receiving andsupporting removable rack 130. In some instances, base 120 comprises aninner wall surface having an annular rim protrusion or shelf thatprovides a surface on which an outer circumferential portion ofremovable rack 130 is seated. Thus seated, removable rack 130 dividesand spatially separates an interior volume of base 120 from an interiorvolume of lid 110. In some instances, removable rack 130 divides theinternal, insulating chamber of apparatus 100 into an upper chamber anda lower chamber, wherein the upper chamber corresponds to the interiorvolume of lid 110 and the lower chamber corresponds to the interiorvolume of base 120.

Base 120 can comprise an inlet valve or port 160 that is inserted intoan opening within a bottom end or portion of base 120. Inlet port 160provides gaseous communication between the lower chamber and theexterior environment surrounding apparatus 100. In some embodiments,inlet port 160 comprises a one-way port, thereby preventing gas withinthe lower chamber from exiting the lower chamber via inlet port 160. Gasor air from the exterior environment enters the lower chamber via inletport 160.

Similarly, lid 110 can comprise an outlet valve or port 150 that isinserted into an opening within a top portion or top surface of lid 110.Outlet port 150 provides gaseous communication between the upper chamberand the exterior environment. In some embodiments, outlet port 150comprises a one-way port, thereby preventing gas from the exteriorenvironment from entering into the upper chamber via outlet port 150.Gas within the upper chamber exits the upper chamber via outlet port150.

Removable rack 130 can comprise any shape, size, and configurationdesired to seat compatibly within device 100 when lid 110 is coupled tobase 120. In some instances, removable rack 130 comprises a perimeteredge that is configured to seat within base 120 on a ledge, shelf, orother annular rim protrusion of base 120. The interface betweenremovable rack 130 and base 120 provides a tight seal thereby preventingor materially restricting passage of gas (typically air) between theupper chamber and the lower chamber. In some instances, removable rack130 comprises one or more holes or gas vents that gaseous communicationbetween the upper and lower chambers. Thus, gas within the lower chambermay flow through removable rack 130 via the one or more gas vents andinto the upper chamber. Similarly, gas within the upper chamber may flowthrough removable rack 130 via the one or more gas vents and into thelower chamber.

In some embodiments, a plurality of sample vials 140 is held or securedwithin wells or openings of removable rack 130. In some instances,sample vials 140 are placed into removable rack 130 prior to placingremovable rack 130 within base 120. In other instances, removable rack130 is first placed into base 120 and subsequently loaded with samplevials 140. Once loaded, base 120 is interlocked with lid 110 therebyconfining removable rack and sample vials within the insulating chamber.

Removable rack 130 may comprise any material or combination of materialscompatible with the teachings of the present invention. For example, insome embodiments removable rack 130 comprises a thermoconductivematerial, such as aluminum, copper, silver, gold, zinc, steel, and/oralloys thereof. In other embodiments, removable rack 130 comprises athermally inert material, such as a weatherable polymer material. Forexample, removable rack 130 is in various embodiments composed ofpolypropylene, polycarbonate, polyvinyl chloride, or polyethylenepolymers. Further, in some embodiments, removable rack 130 comprises acombination or thermoconductive and thermally inert materials, whereinthe thermoconductive materials are in direct contact with the samplevials. As such, heat is transferred from gases within the insulatingchamber to the sample vials via the thermoconductive material.

Referring to FIG. 2, an assembled sample freezing apparatus 200 of thepresent invention is shown in cross section. In some embodiments, aninsulating base 230 supports a removable rack 220 such that theinsulating chamber is divided into an upper chamber 260 and a lowerchamber 250. Further, the placement of removable rack 220 suspendssample vials 215 between upper and lower chambers 250 and 260. Theinsulating base 230 further contains a portal opening into which aninput port 235 is inserted. Insulating base 230 may include one or moreinput ports as may be desired. Input port 235 provides gaseouscommunication between lower chamber 250 and external environment 202.When placed from a warm environment into a colder environment, densergases from the surrounding cold environment enter input port 235 intolower chamber 250. Warmer and less dense gas contained in lower chamber250 is displaced from lower chamber 250 by the denser, cold gas from thecolder environment. As a result, warm air within lower chamber 250 isforced into upper chamber 260 via gas vents 225 in removable rack 220.As warm air from lower chamber 250 enters upper chamber 260, warm airwithin upper chamber 260 is displaced from upper chamber 260 via outletport 205.

In some embodiments, a vacuum is created within upper and lower chambers260 and 250 as gas leaves upper chamber 260 via output port 205. Thisvacuum pressure draws additional cold gas into lower chamber 250 viainput port 235. In other embodiments, the higher density of the cold airforces the lower density warm air from the lower chamber 250 into theupper chamber 260, and subsequently from the upper chamber 260 toexternal environment 202 via output port 205. As cold gas replaceswarmer gas within the upper and lower chambers, heat is removed fromsample vials 215 thereby warming the gas within the chambers. This warmgas is subsequently replaced by additional cold gas that enters lowerchamber 250 via input port 235. The flow of gas through lower and upperchambers 250 and 260 ceases or slows as the temperatures of the gases inthe upper and lower chambers, the sample vials, and removable rack 220reach equilibrium with the exterior environment.

In some embodiments, input vent 235 further comprises a blind terminuscap 245 or deflector cap that causes gases entering lower chamber 250 todeflect laterally through vent ports 240 to fill lower chamber 250uniformly. Removable rack 220 may further include a plurality of gapslocated between the sample vials 215 and the removable rack 220. Thesegaps permit cold gases to pass through removable rack 220 from lowerchamber 250 and into upper chamber 260. Gas pathway flow may also bedirected through a plurality of gas vents 225 in the removable rack forthe purpose of adjusting the temperature change rate of specific samplevials. The size, cross-sectional shape, and placement of gas vents 225can be selected to increase or decrease contact between the gases movingthrough vents 225 and sample vials 215 stored in removable rack 220. Forexample, in some embodiments, gas vents 225 are placed around theperimeter of each sample vial, thereby promoting contact between themigrating gases and the sample vials 215. In other embodiments, gasvents 225 are angled such that gases are directed towards sample vials215 as the gases exit the vents into the upper chamber 260.

During the passage of cold gases over the sample vials, thermal energyis transferred to the cold gas from the warmer vial surface. Thistransfer of heat cools the vial sample and increases the temperature ofthe gases passing over the sample vials. The densities of these gasesare reduced thereby further facilitating movement of the gases throughthe upper chamber 260 and outlet port 205. This process creates acontinuous flow of cold gas over the vials until the temperature of thevials is equal to that of the environment.

Referring to FIG. 3, a view 300 of the insulating base 310, removablerack 330 and sample vials 320 is shown. In some embodiments, gas flowthrough the removable rack is blocked at various positions where theremovable rack 330 forms an interface with insulating base 310. Forexample, removable rack 330 may comprise one or more baffle extensions360. Baffle extension 360 may comprise a webbing of removable rack 330,which provides removable rack 330 with a circumferential perimeter thatcompatibly seats within base 310. Thus, baffle extensions 360 form aseal between removable rack 330 and base 310. This seal further forcesgases within the lower chamber to pass into the upper chamber vial gasvents 350. In other embodiments, gases are directed past the samplevials through the gap 340 between the removable rack 330 and the samplevials 320.

Referring to FIG. 4, results from an experiment are shown, wherein datawas derived from three representative vials placed at positionsrepresenting three concentric distances from the center of a removablerack. The specific vial positions are shown in the drawing inset forvials “A”, “B”, and “C”. The target cooling rate slope of 1 degreeCelsius per minute is represented by the dashed line and depicts thefreezing rate profile (“CC12”) obtained using the Biocision (Larkspur,Calif.) CoolCell∩ freezing device, wherein the sample rack was loadedwith 12 samples to provide the standard target curve. Three solid tracesrepresent the freezing profiles obtained from sample vials A, B, and C,with a 25 degree Celsius starting temperature when a device of theinvention is placed into a −75 degree Celsius environment with theunderside and top vents completely blocked to gas flow.

As shown by the graph, the outermost vial C experiences the fastestfreezing rate, while the middle vial B experiences an intermediatefreezing rate, and the innermost vial A experiences the slowest freezingrate. All freezing rates obtained under these conditions are slower thanthe desired profile provided by the CC12. When the freezing process isrepeated with unblocked vents, the same vials report the additionaltraces shown. The close proximity of the additional traces to thedesired freezing profile shown demonstrates the ability of the venteddevice to equalize the freezing rates within a vial cluster.

Referring to FIG. 5, a sample freezing apparatus 500 of the invention isshown fully assembled and in cross section. In some embodiments, aninsulating base 535 supports a removable rack 520 such that sample vials515 are suspended between upper and lower chambers 565 and 555,respectively. Removable rack 520 is further positioned such that upperchamber 565 is separated from lower chamber 555 by an interface betweenremovable rack 520 and insulating base 535. As with the previousembodiments, insulating base 535 comprises a portal opening into whichan inlet port 540 is inserted. When placed from a warm environment intoa colder environment, the denser gases from the surrounding coldenvironment enter the inlet port 540 thereby displacing the warmer andless dense gas contained in the lower chamber 555 and the upper chamber565. Warmer and less dense gases within the lower and upper chambersexit the upper chamber 565 through outlet port 505.

In some embodiments, gases entering inlet port 540 are deflectedlaterally by a deflector plate 545. Deflector plate 545 may include anysize, shape, and/or configuration to achieve a desired distribution ofcold gases into lower chamber 555. For example, in some embodiments,deflector plate 545 comprises a disc having a plurality of slots oropenings positioned around the perimeter of the disc. In someembodiments, the slots or openings of deflector plate 545 are notaligned with gas vents or gaps of removable rack 520. Further, in someinstances deflector plate 545 comprises a removable component that maybe selectively inserted within an internal cavity or space of insulatingbase 535. In some instances a removable rack and a removable deflectorplate are provided as a matched pair for use in combination to achieve adesired rate of cooling.

In some embodiments, gas pathway flow from lower chamber 555 is directedthrough a central hole 530 in removable rack 520 thereby increasing thegas flow rate for the central vials. The diameter of central hole 530can be selected to optimize and/or equalize the rate of heat transferfrom the vials. Upper vent 505 can have a conical exterior profile, asshown. This profile is useful to prevent accidental blockage of theport, such as by the placement of objects on the top of the assembly 500during the freezing process. Unless the blocking object is purposelybalanced on the exit opening of the vent 505, the object will tip to oneside and unblock the vent opening.

Referring to FIG. 6, a sample freezing apparatus 600 of the invention isshown in frontal cross section with dimensions for specific featuresprovided. In some embodiments, the upper cover 605 is a cylindricalshell constructed from high density polyethylene foam with an outsidediameter of approximately 6.4 inches and a height of approximately 2.750inches. The upper cover further comprises a flat top 610 with athickness of approximately 0.75 inches. The cylindrical walls of cover615 have a thickness of approximately 0.995 inches. In some embodiments,the cylindrical wall of the cover terminates on the lower side in a ringprojection 620 that interlocks by friction fit to an annular ringprojection or protrusion on lower base 630.

Upper cover 605 further comprises a central hole 625 with a diameter ofapproximately one inch that is sized and configured to receive a topvent choke 690. Top vent choke 690 is constructed from a weatherablepolymer material and includes a cylindrical central passageway having adiameter of approximately 0.31 inches. Lower base 630 is constructedfrom the same high density polyethylene foam as the upper cover 605 andhas a cylindrical shape with the same outside diameter as upper cover605. In some embodiments, lower base 630 comprise an overall height ofapproximately 2.350 inches.

In some embodiments, the base floor of the cylinder 635 has a thicknessof approximately 0.5 inches and is supported by four foot extensions 640which have a height of approximately 0.35 inches. Lower base 630 furthercomprises a cylindrical interior shelf 645 that supports the removablesample tube rack 670.

Removable sample tube rack 670 is supported by interior shelf 645 andrestricted in lateral movement by an interior surface 665 of lower base630, wherein the interior surface 665 has a diameter of approximately4.1 inches. Lower base 630 further comprises a vertical cylindricalsurface of interior shelf 645 which comprises a diameter ofapproximately 3 inches and is configured to receive and house an alloydiffusion plate 650. In some embodiments, alloy diffusion plate 650comprises a thickness of approximately 0.105 inches. Alloy diffusionplate 650 further comprises an annular array of slots 660 through whichgases are permitted to pass. Alloy diffusion plate 650 is supported by acylindrical flange 655 of lower base 650, wherein cylindrical flange 655comprise a height of approximately 0.375 inches and serves to form a gasseal with the vertical cylindrical surface of shelf 645.

In some embodiments, removable sample tube rack 670 is configured tohold 30 sample tubes 675, wherein each sample tube 675 comprises anaverage diameter of approximately 0.472 inches, and an average length ofapproximately 1.932 inches. In other embodiments, sample tubes 675comprise a diameter from approximately 0.44 inches to approximately 0.48inches, and a length from approximately 1.8 inches to approximately 1.95inches. The base floor of cylinder 635 further comprises a hole having adiameter of approximately 1 inch that is configured to receive a polymervent 680. Polymer vent 680 generally comprises a weatherable polymermaterial and comprises a central cylindrical passageway 685 having adiameter of approximately 0.625 inches.

Referring now to FIG. 7, a multi-perspective view 700 of the removablesample tube rack 710 is shown. Some embodiments of the present inventioncomprise a removable sample rack 710 having a radial array of 30 samplebays 730, each bay having an opening comprising a diameter ofapproximately 0.481 inches. Removable sample rack 710 further comprisesa central vent hole 720 having a diameter of approximately 0.449 inches.Central vent hole 720 is provided for the purpose of directing gas flowthrough removable sample rack 710 during a freezing process.

In some embodiments, removable sample rack 710 further comprises two ormore side contours to facilitate handling of the rack. For example, insome embodiments removable sample rack 710 comprises six lobespositioned in a radial array around the outer perimeter of the rack.Each lobe of removable sample rack 710 comprises a repeating unit of 5sample bays 760 that are arranged at rotational intervals ofapproximately 60 degrees around central vent hole 720. In someembodiments, removable sample rack comprises a maximum outer dimensionof approximately 4.087 inches, and a maximum height of approximately0.800 inches.

In some embodiments, an outer skirt of removable sample rack 710terminates in a planar lower edge 740 which is configured to form a gasbarrier seal when rack 710 is seated on cylindrical interior shelf 645,as described in FIG. 6. Each sample bay 730 comprises a lower pair ofconically tapered grip extensions 750, which terminate to form a bottomfoot upon which a bottom surface of the sample vial rests. Uponinsertion of a sample vial into sample bay 730, the tapered gripextensions 750 are displaced outwardly thus providing spring tension onthe outer wall surface of the vial to retain and secure the vial withinthe sample bay 730 in an upright, centered position. Spaces or gapsbetween the outer wall surface of the sample vial, the sample bay 730and the tapered grip extensions 750 allow for gas flow between thesample vial rack and the sample vial.

In some embodiments, each lobe of removable sample rack 760 comprisesfive sample bays 730, each sample bay 730 having a pair of tapered gripextensions 750. The orientation of the five sets of tapered gripextensions 750 for each lobe is identical. In some embodiments, sixlobes are positioned in a radial array centered on a central vent hole720. As such, the orientation for the tapered grip extensions 750 foreach lobe is in approximate radial alignment with central vent hole 720.In other words, the orientation of the tapered grip extensions 750 for afirst lobe is different that the orientation of the tapered gripextensions 750 for an adjacent lobe. This configuration symmetricallydistributes the distorting forces from the expanded or outwardly biasedtapered grip extension for each lobe, thereby insuring a planarorientation or field of the planar lower edge 740 of removable samplerack 710.

The invention claimed is:
 1. A device for freezing two or more samplesstored within vials, said device comprising: a base having a top end, abottom end, and a lower chamber extending therebetween and having afirst interior volume, the top end having an opening and the bottom endhaving an inlet port; a cover having a top end, a bottom end, and anupper chamber extending therebetween and having a second interiorvolume, the top end of the cover having an outlet port and the bottomend of the cover having an opening, the bottom end of the cover beingconfigured to interconnect with the top end of the base; a sample rackdisposed between the base and the cover and configured to receive thevials, wherein the sample rack divides the lower chamber from the upperchamber when the cover is interconnected with the base; an interiorenvironment comprising the first and second interior volumes when thecover is interconnected with the base, the interior environment havingan initial interior temperature; and a gas density gradient within theinterior environment from the inlet port to the outlet port when thedevice is placed in an exterior environment having an environment gascomprising an ambient temperature that is less than the initial interiortemperature, wherein heat is removed from the initial interiortemperature in part by passive gas diffusion promoted by the gas densitygradient.
 2. The device of claim 1, wherein the heat is removed via theoutlet port as the environment gas is introduced to the interiorenvironment via the inlet port.
 3. The device of claim 1, wherein thepassive gas diffusion provides a uniform freezing rate for the two ormore samples.
 4. The device of claim 1, further comprising a gas flowpathway through the interior environment.
 5. The device of claim 4,wherein a portion of the sample rack blocks a portion of the gas flowpathway.
 6. The device of claim 5, wherein the portion of the samplerack is a perimeter surface.
 7. The device of claim 5, wherein theportion of the sample rack is an interface surface between at least oneof the base and the cover.
 8. The device of claim 5, wherein the portionof the sample rack is an interior surface.
 9. A method for freezing aspecimen, comprising: introducing a sample into a sample rack; disposingthe sample rack into a sample freezing device comprising: a basecontainer having a top end, a bottom end, and a lower chamber extendingtherebetween, the top end having an opening and the bottom end having aninlet port; a cover having a top end, a bottom end, and an upper chamberextending therebetween, the top end of the cover having an outlet portand the bottom end of the cover having an opening, the bottom end of thecover being configured to interconnect with the top end of the basecontainer, wherein the sample rack is disposed between the base and thecover, the sample rack comprising a top surface and a bottom surfaceforming an interface with the base container, wherein the sample rackdivides the lower chamber from the upper chamber when the cover isinterconnected with the base container to provide an assembled samplefreezing device having an interior environment comprising a firstenvironment gas having an interior temperature; placing the assembledsample freezing device into an environment comprising a secondenvironment gas having an ambient temperature that is less than theinterior temperature; and introducing the second environment gas intothe interior environment via the inlet port, wherein the secondenvironment gas displaces the first environment gas from the interiorenvironment via the outlet port.
 10. The method of claim 9, wherein thesecond environment is an archival storage site.
 11. The method of claim9, wherein the second environment is a freezer.
 12. The method of claim9, further comprising a step for blocking a gas flow through the samplerack where the sample rack forms an interface with the base container.13. The method of claim 9, further comprising a step for providing a gasflow through the sample rack at one or more positions proximate to thesample.
 14. The method of claim 9, wherein at least one of the basecontainer and the cover comprise a thermo-insulating material.
 15. Themethod of claim 14, wherein the thermo-insulating material is selectedfrom the group consisting of polyethylene, polystyrene, polyurethanefoam.
 16. The method of claim 9, wherein the sample rack comprises atleast one of a thermoconductive material and a thermally inert material.17. The method of claim 9, wherein the first environment gas comprises adensity that is less than a density of the second environment gas.
 18. Asample freezing device, comprising: a base having a top end, a bottomend, and a lower chamber extending therebetween, the top end having anopening and the bottom end having an inlet port; a cover having a topend, a bottom end, and an upper chamber extending therebetween, the topend of the cover having an outlet port and the bottom end of the coverhaving an opening, the bottom end of the cover being configured tointerconnect with the top end of the base; and a sample rack disposedbetween the base and the cover, the sample rack comprising a top surfaceand a bottom surface, the sample rack forming an interface with at leastone of the base and the cover, wherein the sample rack divides the lowerchamber from the upper chamber when the cover is interconnected with thebase and wherein a gas flow through the sample rack is blocked at theinterface.
 19. The device of claim 18, wherein the gas flow is furtherblocked by an interior surface of the sample rack.
 20. The device ofclaim 18, wherein the sample rack further comprises: a sample bay forreceiving a sample vial; and a gas vent in proximity to the sample bay.